linux-kernel - Re: (subset) [PATCH 20/32] vfs: factor out inode hash head calculation

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Message-ID: <ZG1D4gvpkFjZVMcL@dread.disaster.area>
Date:   Wed, 24 May 2023 08:53:22 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Dave Chinner <dchinner@...hat.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-bcachefs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: (subset) [PATCH 20/32] vfs: factor out inode hash head
 calculation

On Tue, May 23, 2023 at 11:27:06AM +0200, Christian Brauner wrote:
> On Tue, 09 May 2023 12:56:45 -0400, Kent Overstreet wrote:
> > In preparation for changing the inode hash table implementation.
> >
> >
> 
> This is interesting completely independent of bcachefs so we should give
> it some testing.
> 
> ---
> 
> Applied to the vfs.unstable.inode-hash branch of the vfs/vfs.git tree.
> Patches in the vfs.unstable.inode-hash branch should appear in linux-next soon.
> 
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
> 
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs.unstable.inode-hash
> 
> [20/32] vfs: factor out inode hash head calculation
>         https://git.kernel.org/vfs/vfs/c/b54a4516146d

Hi Christian - I suspect you should pull the latest version of these
patches from:

git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs.git vfs-scale

The commit messages are more recent and complete, and I've been
testing the branch in all my test kernels since 6.4-rc1 without
issues.

There's also the dlist-lock stuff for avoiding s_inode_list_lock
contention in that branch. Once the global hash lock is removed,
the s_inode_list_lock is the only global lock in the inode
instantiation and reclaim paths. It nests inside the hash locks, so
all the contention is currently taken on the hash locks - remove the
global hash locks and we just contend on the next global cache
line and the workload doesn't go any faster.

i.e. to see the full benefit of the inode hash lock contention
reduction, we also need the sb->s_inode_list_lock contention to be
fixed....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com